Magilla......I think "Executive" made a good point about your coach and carrying that weight. Actually, if you coach was shorter, it would probably work better. You're looking at adding a lot of weight onto the rear of a long gas coach, with a long overhang, already pushing the limits of the chassis.
Initially you were talking 500-600 pounds plus the hitch, but have revised it a little as many have said that's too much. You need to be honest with yourself.....are you going to really push that much weight, with possibly two smaller bikes or one larger one?
Anything above 200-300 pounds will need some serious added on welding and hitch work. You're also talking about pushing a motorcycle weighing several hundred pounds up a ramp and balancing it. Unless you're really built like Magilla Gorilla, that can be tough.
You might want to buy one of the Harbor Freight rear storage racks (aluminum one) as a cheap experiment and put 500 pounds in it and see how it affects your coach.
You may want to rethink the trailer thing because you're looking at spending a lot of money to put on such a substantial carrier. I bought a folding trailer that stored standing up in my side yard (2' x 5') footprint. It held my 1100 Honda VTX or two smaller bikes. It was easy to maneuver at a campsite. I also set it up so the bike could be loaded on it when not attached to the coach.
Just some thoughts......you're getting into some engineering issues with the size you want to carry.